1. Field of the Invention.
The present invention relates to bar code readers generally and more particularly to a novel reading head for such devices and one which may be used with illuminating light of different wavelengths and for reading different bar codes having substantially different widths of bars.
2. Background Art.
Bar codes have found application in a wide variety of applications as an information source, typically for digital processors. Such bar codes are used at point-of-sale in merchandising for pricing and inventory count, in controlled personnel access systems, and in manufacturing for work-in-process and inventory control, to name only a few applications. The bar codes themselves comprise a series of parallel lines, typically in the range of about 1/8" to 1" in height and from about 1 to 50 mils in thickness, arrayed on a contrasting background. The lines may variously have unequal spacings and/or unequal thicknesses, with the variations in spacing and/or thickness determined by the information "stored" in the bar code. A bar code is "read" by serially illuminating the bars, with the bars absorbing the light and the background reflecting the light. The resulting pattern of reflection and nonreflection is sensed by a light detecting device which provides input to the digital processor. The reader head may be of the type that is passed over the bar code or of the type with which the bar code is moved passed the reading head, such as might be used with a personal identification card. While the present invention is directed generally toward the latter type, it will be understood that it may be modified and applied to the former type, as well, or even where there is no relative motion, by one having ordinary skill in the art.
One class of conventional bar code reader heads comprises those that are point detectors; that is, the detecting device is focused at a single, relatively small point. Such a reader head is described, for example, in U.S. Pat. No. 4,143,809, to Uebbing et al. These readers have two major disadvantages. First, since the detector is focused at a point on the bar code, the reader has a very short depth of field, possibly on the order of 5 mils at a distance of 300 mils from the focusing lens. This means that the substrate carrying the bar code must be accurately placed in distance from the lens in order to provide good resolution. Second, if a bar on the bar code is unintentionally broken or otherwise defective at the point of focus, it will be detected as being absent, thus providing misinformation to the data processor.
A further limitation of conventional devices is that no known bar code reader heads have the desirable ability to employ either visible or infrared illuminating light in the same device, although such would be advantageous in some applications. Typically, visible red light generated by a light emitting diode (LED) is used for reading visible bar codes, or bar codes that cannot be read with infrared radiation such as thermally printed bar codes with low carbon content. These bar codes are useful where it is convenient to be able to visually read the bar codes or to identify them as such. However, in some applications, it is necessary to read "masked" bar codes, such as those described in U.S. Pat. No. 4,359,633 to Bianco, titled "Spectrally-Limited Bar-Code Label and Identification Card". In the latter applications, infrared illumination is used to read bar codes that cannot be read visually.
Additionally, no known bar code reader heads have the desirable ability to be adjusted for use with different bar codes having bars of substantially different widths.
A further limitation of known bar code reader heads is that they are of relatively complicated manufacture and require relatively precise adjustment during or after manufacture.
Accordingly, it is a principal object of the present invention to provide a bar code reader head that may be used with more than one frequency range of illuminating light.
It is a further object of the present invention to provide a bar code reader head that can be adjusted for use with different bar codes having bars of substantially different widths.
It is a another object of the present invention to provide a bar code reader head that has a relatively deep depth of field and which reads a substantial height of each bar.
It is an additional object of the present invention to provide a bar code reader head achieving the above objects while being of relatively simple manufacture and without requiring relatively precise adjustments either during or after manufacture.
Other objects of the present invention will, in part, be obvious and will, in part, appear in the following description.